Nowe stanowisko egzotyków z warstw krośnieńskich w okolicy Ustrzyk Górnych (Bieszczady)

Abstract

A New occurrence of exotic blocks in the Krosno Beds near Ustrzyki Górne (Bieszczady range, Polish Eastern Carpathians) A new occurence of exotic blocks in the Krosno Beds was found by A. K. Tokarski in 1968. K. Mochnacka elaborated the pétrographie description of these blocks. The exotic blocks occur in a small tributary of the Zakopaniec creek near the touristic trail from Ustrzyki Górne to Mt. Tarnica and Mt. Halicz, (Fig. 1) c.250 m above the top of the youngest complex of the Otryt sandstone, in the north-eastern limb of a Brzeżna syncline (Fig. 2) built of the middle and upper division of the Lower Krosno Beds, in the stratigraphie division of K. Zytko (1968). Petrographically, the exotic blocks consist of schist, steelgrey coloured, with single garnet crystals. Locally, the rock is „saturated” with silica, and crossed by veins of white quartz, a few cm thick. Microscopically the rock was determined as chlorite-muscovite schist with garnets. The mineral composition is presented in Table 1 in the Polish text. The rock has a granolepidoblastic texture and schistose structure, and is built of alternating streaks of platy minerals and quartz. Muscovite is the predominant mica and forms intergrowths with biotite and chlorite. Inclusions of leucoxene, opaque minerals, apatite and zonal tourmaline as well as of a mineral resembling epidote, are present. The scattered garnet grains are intergrown with biotite and chlorite flakes and small aggregates of sericite. The described rocks was formed by processes of regional metamorphism, probably in the greenstone facies. Tentatively it can be assigned to the quartz-albite-epidote-almandine subfacies, differing however from the typical development, as plagioclases are absent in the rock. Several occurrences of exotic blocks in the Krosno beds are known along the south-western margin of the Central Synclinorium, and three of these: at Baligród (A. Ślączka, 1963, A. Ślączka and T. Wieser, 1962), at Bukowiec (A. Ślączka, 1961) and at Riszkania (W. W. Danysz, 1966) seem to occur in a similar stratigraphie position. The accumulation of the exotic blocks at these localities as well as at Ustrzyki Górne, were formed most probably by submarine slides from the western prolongation of the Maramuresz or Rachow massif (A. Ślączka, 1961, 1963) and possibly are related with the facies of the Otryt sandstone (S. Dżułyński and A. Ślączka, 1958). All these rocks are petrographically similar. It is possible that they are marking an exotic block zone, which could be used for stratigraphie correlation of the Krosno Beds in the area of the Bieszczady range.